Method of casting under pressure in dentistry



Jan. 31, 1928.

K. INAMI METHOD OF CASTING UNDER PRESSURE IN DENTISTRY Original Filed Oct. 31, 1925 a; INVENTOR ATTORNEYS Patented Jan. 31, 1928.

UNITED STATES xAxUJmo mam,

or mono, new.

METHOD OF CASTING UNDER PRESSURE IN DENTISTRY.

Original application filed October 31, 1925, Serial No. 66,041. bivided and this application filed January 22, 1927.

This invention relates to improvements in methods of casting under pressure in dental prosthesis and the present application constitutes a division of my application Serial No. 66,041, liled October 31, 1925. More particularly, this invention relates to a method of forming smooth castings of exact size in such a manner that only a short heating is required and the rapid escapeof gases is facilitated.

The methods now being employed, while less undesirable for small castings than for large castings, have many disadvantages when employed in the preparation of castings requiring accurate measurement and surfaces free from roughness. Because of the manner in which the castings are formed as well as the difliculties encountered in adapting the present apparatus to work of an exact nature, the castings produced are usually thicker than the wax pattern, rough surfaced, and more or less deformed so that they do not fit properly; Sometimes, the castings are so badly formed as to require several recastings before a good specimen is obtained.

Hitherto the practice has been to form a mould by pushing the prepared wax pattern into the plastic investment compound and allowing the latter to set after it has completely surrounded the pattern. The preparation of the pattern is usually done on a model. Since. the wax is soft, removal from the model and subsequent handling preparatory to inserting the pattern in the investment compound invariably results in deformation of the pattern. Then, as the compound sets, the pattern is further deformed because of the shrinkage of the compound, and cracks are formed in the surface of the mould. If the mould is formed with a small number of comparatively thick sprues, because of the nature of the flask, the bulk of the casting metal is increased and the amount of shrinkage is very large and the resulting casting is considerably distorted. On the other hand, if the crucible formed in the top of the flask is too shallow suificient metal cannot be properly kept in its molten stage and all parts of the mould will not be filled.

To overcome'such difficulties as have been pointed out, I have developed a method of successfully preparing dental castings of exact size with even surfaces. The various Serial No. 162,697.

features of my method when applied in the preparation of the upper jaw denture, as an block,

Fig. 2 is a perspective View showing how the plastic investment compound is poured around the pattern,

Fig. 3 is a perspective view of the cast formed by the investment compound,

Fi 4 is a sectional perspective view showing t ewax pattern imbedded in the casting mould,

, Fig. 5 is a sectional perspective view of the wax pattern after the model block has been removed,

Fig. 6 is a perspective view of a, flask,

Fig. 7 is a perspective view of a pouring crucible pattern,

Fig. 8 is a-vertical sectional view showing a the casting mould,

Fig. 9 is a vertical sectional View showing the flask in a heater,

Fig. 10 is a vertical sectional view showing the application of pressure during the casting operation.

In the accompanying drawings, a model of an upper jaw cast of plaster, artificial stone, or other suitable material is shown at a. A pattern of a gold plate to be cast, shown at b, is formed by pressing wax sheets of the proper thickness upon the surface of the model a. U-shaped wax wires 0, which later form shoulders for the vulcanite backing of the denture, are arranged and attached around the outer edge of the pattern I). A plurality of slender wax wires d, for forming sprues, are attached at their one end to the U-shaped wax wires 0 as well as'to other parts of the pattern b, and are bunched together at their other end in order to form a closely arranged group of pouring holes. Surrounding the pattern b and secured to the model block a is a shell e into which is poured the casting compound. Thegrouped wires 01 project from the apex of the shell, as" shown in Fig. 2.

With the shell 6 in the positionshown in Fig. 2, investment compound of the proper consistency is poured in through the opening in the upper side. The compound is carefully packed around the wax pattern and wires and then allowed to harden.

After the compound has set, the shell 6 and model block a may be removed and the mould M turned with the wax pattern to the top, as shown in Fig. 4. The surplus material may then be scraped away, as shown by f in Fig. 5, and a layer of plastic compound g applied over the pattern b and allowed to harden. The pattern and wires are now completely imbedded in the hardened compound. The tip of the mould M is cut down to a size permitting it to be inserted in the centralhole of the pouring crucible pattern, as explained later.

A flask ada' ted to receive the pyramidal mould M an consisting of a cylindrical part it, lattice portion j, and semi-elliptical rim 2' is shown at F in Fig. 6. The cylindrical collar serves as a seat for a pouring crucible pattern. The semi-elliptical rim i is considerably larger than the cylindrical collar in order to accommodate the large end of the mould M. To facilitate the escape of gases, rods j are used to connect the collar and rim and provide the openings 1a through which the gases can readily pass during heating. A pouring crucible pattern P, illustrated in Fig. 7 is provided with a conical projection n and a shallow groove m on its one face. The roove is of such a size as to fit over the co lar h of the flask while the opening 0 in the conical ortion has a diameter equal to the small en of the. mould M.

To assemble the mould M in the flask F, as shown in Fig. 8, the flask is inverted upon the crucible pattern P and a paper or rubber guard 72 placed around the lattice bars 7'.

The mould M is then plablid in the flask withthe small end of the mould projectin into the hole 0 in the crucible pattern. Ihvestment compound of the pro er consistency is slowly worked into the flas and around the mould until the flask is filled to the rim z. The mould M is thus completely surrounded by the compound with the exception of the small portion at the a ex. After the compound has hardened, t e guard paper p is removed and the crucible pattern taken off, the .portion of the mould. M extending through the hole being broken oil when the pattern is removed.

The preparation of the mould for casting is thus carried out in three stages. First, the investment compound is applied to the wax pattern positioned on the model block. When the compound has hardened,'the model block is removed, and the cap portion of investment compound added. Aftemhe cap portion has hardened, the entire mouldM is inserted in the flask and packed with further, investment compound. Considering the efl'ect of the several stages u on the wax pattern, when the shrinkage o the first application of compound 7 tends to deform the wax pattern such action will be prevented by the rigidity of the model block. Then when the shrinkage of the cap portion of compound tends to deform the pattern deformation will be prevented by the hardened compound portion in The wax pattern is thus not influenced by the shrinkage of the various layers of the investment compound. After the mould is packed in the flask and heated to the necessary high temperature, fissures are produced in the compound because of its nature, but such fissures do not alter the relative position of the two parts of the mould M. Furthermore, since the cap portion 9' is locked upon the portion f by reason of the overlapping edges, no movement between the two parts will occur due to the expansion and contraction of the compound.

The filled flask is placed in a heater, as shown in Fig. 9, with the crucible upward and heated, slowly at first and gradually stronger until the mould is dry. After the mould is dry the heat is continued from the Bunson burner until the wax wires and pattern have completely vaporized and passed up out of the mould, leaving the pattern cavity 7* and the sprues 8. The mould is then ready for casting.

At this stage, of the metal to be used to the castin is one having a low melting point, such as a uminum, the casting work can be commenced immediately. If gold is used. however, the mould must be heated still further. To raise the heat to the point necessary, charcoal is piled around the flask and both bunsen and charcoal burned together. When on looking through a peep hole 3 in the lid :1: of the heater the flask is seen to be heated red hot, the upper portion t of the heater is removed and a lid '2) placed over the remaining portion a as shown in Fig. 10. The desired metal is then placed in the crucible and smelted with a torch as indicated. When the metal is completely melted and running into the sprues, a pressure lid W, or other pressure means, is placed over the crucible. Under the pressure thus formed, the

molten metal completely fills the cavities in the mould and produces a compact and smooth surfaced casting of the same size as the wax pattern b.

Because the greater part of the flask is formed of open lattice work, the escape of gases, either xisting or generated during casting, is gre tly facilitated with the result that the formation of cracks and bubbles in the surface of the cavity is substantially eliminated. In most moulds, a clearance due to the shrinkage of the metal is apt to cause the thin casting of shape. The provision of pressure in the present type of mould prevents such a deformation because the downward force on the compound portion [doses up any clearance to twist and curl out i I that might be caused between the two seccasting.

tions of the mould. In addition, since the crucible is ingeniously formed in the mould and communicates with the casting cavity through the numerous sprues uniformly dis,- tributed throughout the cavity, the molten metal flows steadily and quickly into the mould without forming irregularities in the casting. Numerous small sprues are far better than a few large sprues because the thin casting is less apt to be affected by the shrinkage of the small amount of metal con-. tained in the small sprucs than by the shrinkage of the large quantity of metal contained in the large sprues. Then too, a large number of sprues can be better distributed over the casting. Because of the simplicity of the apparatus and the-.manner in which the mould is prepared the heating means need not be extensive. The heater can be constructed and operated very inexpensively and is not excessively injurious in its effects upon the flask. Either gas or charcoal may be used in the heater by virtue of its sturdy construction. i

It is to be understood that various modifications may be made in the method as described and illustrated without departing from the spirit and scope of the invention as defined by the following claims.

I claim:

1. A method of producing castings for dental prosthesis comprising, placing a wax pattern on asuitable model, applying investment compound to the exposed surface of said pattern, removing the frnodel', applying investment compound to the other surface of the wax pattern to form a mould, heating the mould, and pouring suitable casting metal into the mould to form a casting.

2. A method of producing castings for dental prosthesis comprising, placing a Wax pattern on a model, affixing a plurality of fine wax wires to the pattern,-applying investment compound to one surface of the pattern, removing the model, applying in-- vestment compound to the other surface of the pattern to form a mould, placing the mould in a reticulated flask, heating the mould while in the flask, and pouring suitable casting metal into the mould to form a 3. A method of' producing castings for dental prosthesis comprising, placing a wax pattern on a model, affixing a large number of fine wax wires to the pattern,, gathering the free ends of the wires together, applying investment compound to one surface of the pattern to enclose the wires, removing the model, applying investment compound to the other surface of the pattern to form a mould, placing the mould in a reticulated flask, forming a pouring" crucible for the mould while in the flask, heating the mould in the flask, and pouring suitable casting metal into the mould to form a casting.

4. A method of producing castings for dental prosthesis comprising, placing a Wax plying investment compound to the other.

surface of the pattern to form a mould, reducing the body of the mould to form a tapered neck portion enclosing the bunched wires, positioningthe mould in a rccticulated flask by means of said tapered neck portion, heating the mould in the flask, and pouring suitable casting metal into the mould under pressure to form a casting.

5. A method of producing castings for dental prosthesis comprising, placing a wax pattern on a model, applying investment compound to one surface of the pattern, removing the model, applying investment compound to the other surface of the pattern to form a mould, said second application of investment compound surrounding at least a portion of said first application, positioning the mould in a flask, packing said flask with investment compound shaped at one end of the flask to form a pouring crucible for the mould, heating the mould in the flask, and "pouring suitable casting metal .under pressure into the mould to form a casting.

6. A method of producing castings for dental prosthesis comprising, placing a wax pattern on a model, applying investment compound to one surface of the pattern, removing the model, applying investment compoundto the other surface of the pattern to form a mould, packing the mould with investment compound 1n a flask, heating the "flask and mould in a furnace to vaporize the wax pattern, heating the mould still further, and pouring suitable casting metal into themould under pressure to form a casting.

In testimony whereof I afiix my signature.

KAKUJIRO INAMI. 

